Persistent and volatile pollutants – including certain pesticides, industrial chemicals and heavy metals – evaporate out of the soil in warmer countries where they are still used, and travel in the atmosphere toward cooler areas, condensing out again when the temperature drops. The process, repeated in "hops", can carry them thousands of kilometres in a matter of days.

Canada's cold climate puts it at the receiving end of this process, with measurable concentrations of DDT, toxaphene, chlordane, PCBs, and mercury found in both the Great Lakes and the Arctic. Ingested by fish and other species, the chemicals travel up the food chain, accumulating in the fatty tissue of predatory animals, including people. Some of these pollutants are linked with developmental and reproductive impacts on wildlife, and may have similar effects on humans. The consequences may be serious for Native people in the North, because traditional food sources are being contaminated.

Environment Canada scientists measure and monitor concentrations of these toxic chemicals to learn more about how they are exchanged among air, land and water. Similar studies being carried out in Russia – both by Canadian scientists and by Russian colleagues using analytical equipment Canada donated several years ago – are yielding useful data for global comparisons, and providing additional insight into the impact on shared resources such as the Arctic Ocean.

An important breakthrough has been the recent development of a technique for identifying the age and source of some of these chemicals. Certain persistent organic pollutants (POPs) have right- and left-handed molecules that are mirror images of one another. While new formulations tend to have equal amounts of both, differences in the way these molecules are metabolized by microbes and enzymes in the biological system change this ratio as the chemical ages. The tracers show the grasshopper effect quite clearly. By separating them, it should be possible to determine how long they have been travelling, and whether they have spent time on land or in water. By matching them with weather records, scientists should also be able to find out where the chemicals are from.

In the figure below, approximately 10% of the highest cases of p,p'-DDT (a component of DDT) arriving at two Integrated Atmospheric Deposition Network stations on the Great Lakes are tracked back to potential sources in the south using weather records.

Information obtained through these and other Canadian studies is the foundation of international negotiations for global bans on certain of these toxics. Canada is playing a leadership role in these efforts. They include the recent negotiation of protocols for POPs and heavy metals under the United Nations Economic Commission for Europe – to be signed this June – and other initiatives are now being launched with other parts of the world through the United Nations Environment Programme. Canada's work in the Great Lakes and Arctic provides powerful evidence that persistent toxic pollutants are travelling long distances, and the efforts have raised global awareness of an important issue.